MARTINEZ — A man brandishing a handgun held up a gas station Monday evening, and police said the presence of trick-or-treaters in the area hampered their search for the robber.

At 7:30 p.m. the man walked into the Flex Oil station in the 6700 block of Alhambra Avenue, pointed a gun at a clerk and demanded money. He took an undisclosed amount of cash and fled toward an adjacent shopping center. No one was injured.

The robber was described as a white man in his 20s, 6 feet tall and wearing a black hooded sweatshirt and dark-colored jeans.

Anyone with information about the robbery can contact investigators at 925-372-3450.

Violent police encounters in California last year led to the deaths of 157 people and six officers, the state attorney general’s office said Thursday in a report that provides the first statewide tally on police use-of-force incidents.

At 6:03 p.m. Wednesday, police responded to reports of the robbery at the facility, 2301 Bancroft way, and learned that a man who snuck into the facility and began prowling through the building, taking cell phones and wallets from victims.

Investigators’ efforts to solve the case led to the arrests of Pablo Mendoza, 25, of Hayward, Brandon Follings, 26, of Oakland and Valeria Boden, 26, of Alameda, the Alameda County Sheriff’s Office said Thursday.